Heat exchangers are commonly used in heat recovery systems to conserve energy. Heat exchangers may be employed as air pre-heaters, for example, for furnaces, boilers and the like. In such systems, heat energy commonly is to be transferred from a hot flue gas to a stream of fresh combustion air. Extreme temperatures and highly corrosive conditions often are encountered. Desirably, the two fluid streams flowing through the heat exchanger are substantially sealed from one another.
Cross-flow plate-type heat exchangers commonly employ a series of spaced, parallel plates carried between parallel end walls, with corner posts serving to rigidly connect the end walls. A first fluid flows through alternate spaces between the plates in a first path, and a second fluid flows in a second perpendicular path through alternate spaces adjacent the spaces of first path. Corner seals are provided to seal the aligned corners of the heat exchange plates to prevent mixing of the two fluids.
The heat exchanger plates are supported laterally in their planes by the corner posts, and the corner seals accommodate to some extent plate movement generated by thermal expansion and contraction of the plates in their planes. Substantial leakage from one fluid stream to the other may occur between the aligned plate corners and the corner posts. The rate of leakage usually increases with use, and leakage rates of thirty percent or more of the volume of one stream into the other are not uncommon. Resilient members may be employed between the aligned corners of the plates and the closely adjacent surfaces of the corner posts to support the plates and to seal the space between the corner post and the aligned plate corners. The resilient members should seal this path but should be capable of simultaneously absorbing, through movement, the substantial expansion of the plates in their planes and the high compressive forces of plate expansion without taking on a permanent compression set. Also, depending upon orientation of the heat exchanger, the resilient members may be required to bear the weight of the heat exchanger plates, which may be substantial.